Hi guys, hope you can help

Got a 1994 M plate Xantia and have a problem with the central locking...

When using the key in the drivers door lock the central locking is not
activated at all, i.e. just the drivers door locks and unlocks. This also
doesn't appear to activate the immobiliser keypad as I dont need to re-enter
my code to start the car (?).

If I use the key in the passenger door then all the doors lock, then
immediately unlock (including the drivers door). The immobliser keypad is
activated.

For some reason the remote 'blip' doesn't work at all (although the little
red led on the key lights up).

Could the problem with the locking be to do with the drivers door lock or
the lock servo?

Do you think replacing the drivers door lock would remedy this?

Thanks in advance for any suggestions